Phase shifting system useable in phased array for discriminating radar echoes from raindrops

ABSTRACT

An array of phase shifting elements each of which is suitable for forming a microwave lens in a radar tracking system and for attenuating radar echoes from raindrops. Each phase shifting element comprises a ferrite rod enclosed by a metallic overlay for providing phase shift in a circular polarization mode, current carrying windings for impressing a magnetic field within the ferrite rod, a pair of nonreciprocal quarter wave plates biased by permanent magnets and located at the ends of the ferrite rod, a vane adjacent the back end of the ferrite rod for absorbing radiant energy having a polarization associated with rainfall reflections, an impedance matching section at the back end of the phase shifting element and a quarter wave plate at the front end of the phase shifting element. Means are also disclosed for focussing the array of phase shifters for airport surveillance.

United States Patent 91 Mohr et al.

[.11 3,736,535 1 May 29,1973

[75] Inventors: Max C. Mohr, Chelmsford; Leo Malancon, Dover; Stephen R. Monaghan, Harvard, all of Mass.

[73] Assignee: Raytheon Company, Lexington,

Mass.

[22] Filed: May I, 1972 [21] Appl. No.: 249,125

[52] US. Cl. ..333/3l A, 333/21 A, 333/24.i, 333/33, 343/777,;543/854, 343/100 SA 51 in c|..... ..H0lp 1/18 '[58] FieidofSearch ..333/21A,24.l,31A;

['56] References Cited ABSORBING VANE 8mm:

26 NON-RECIPROCAL 4 PLATE MATCHING SECTION 3,698,008 l0/l972 Roberts et al. ..333/24.i X

Primary Examiner--Paui L. Gensler Attorney-Milton D. Bartlett, Joseph D. Pannone, Herbert W. Arnold and David M. Warren "Es '71 ABSTRACT An array of phase shifting elements each of which is suitable for forming a microwave lens in a radartracking system and for attenuating radar echoes from raindrops. Each phase shifting element comprises a ferrite rod enclosed by a metallic'overlay for providing phase shift in a circular, polarization mode, current carrying windings for impressing a magnetic field within the ferrite rod, a pair of nonreciprocal quarter wave plates biased by permanent magnets and located at the ends of the ferrite rod, a vane adjacent the back end of the ferrite rod for absorbing radiant energy having a polarization associated withrainfall reflections, an impedance matching section at the back end of the phase shifting element and a quarter wave plate at the front end of the phase shifting element. Means are also disclosed for focussing the array of phase shifters for airport surveillance.

14 Claims, 7 Drawing Figures FERRITFE PHASE \RECIPROCAL 6 PLATE Patented May 29, 1973 3 Sheets-Sheet 2 Patented May 29, 1973 3 Sheets-Sheet 5 BACKGROUND OF THE INVENTION" This invention relates to an array of phase shifting elements, and more particularly to coupling techniques and impedance matching techniques to permit operation of the phase shifters in the lens of a microwave optical system.

' Phase shifting elements have been employed in phased .array antennas for generating a steerable beam of radiation. Transmission type phase shifters wherein the radiant energy enters at one end of the phase shifter and exits at the opposite end are utilized in lens type phased array antennas. While a variety of such phase shifters have been built'such as, for example, digital diode type elements providing quantized amounts of phase shift in response to energization of specific pairs of diodes, and ferrite type phase shifters which provide a variable amount of phase shift in response to energization by a magnetic field, such phase shifters are built for specificapplications and are, accordingly, not generally suitable for all applications. In particular, in commercial type equipment it is desirable to minimize the number of phase shifting elements to be utilized in a lens to reduce the cost .of the lens and the complexity of the control equipment which controls the phase in each of the phase shifting elements. And where the rectangular waveguide and cross-linked polystyrene sections placed along the short walls of the rectangular waveguide. The rear impedance matching system further provides for a substantial spacing between adjacent phase shifting elements, up to three-quarters of a wavelength, by means of pins inserted between the broad walls of the rectangular waveguides of adjacent phase shifting elements, these pins being directed rearequipment is to be utilized in an aircraft tracking situation where rainfall may obscure the image of an aircraft, the array of phase shifting elements should provide a measure of discrimination between raindrops and aircraft. Furthermore, in order to minimize the amount of power required by the phase control equipment as well as to simplify such equipment, the phase shifting elements should have the facility'for retaining a given phase shift, even after a control signal is removed.

SUMMARY OF THE INVENTION The aforementioned problems are overcome and other features are provided by an array of phase shift-' ing elements in accordance with the invention wherein each phase shifting-element is provided with a phase shifter section having the form of a circularly polarized Faraday rotator, a polarization sensitive RF (radio frequency) load, an impedance matching system, and a plurality of nonreciprocal quarter wave plates which coact to provide a reciprocal phase shifting element. The circularly polarized Faraday rotator of the phase shifting section comprises a ferrite rod enclosed by a metallic overlay and is energized by a magnetic field induced by currents in coils of wire wound around the ferrite rod. Energization of the ferrite rod is provided even after a cessation of these electric currents by means of a latching feature provided by a square hysteresis loop characteristic of the ferrite rod.

An impedance matching system at the rear of each of the phase shifting elements comprises a section of waveguide, preferably rectangular, coupled to theferrite rod via a dielectric section having a stepped surface at its interface with the rectangular waveguide, there being furthermore a post placed in the broad wall of the wardly of the elements and having axes parallel to the element axes. In addition, the matching systemfor each phase shifting element comprises a collar, having an axial length of one-quarter wave-length, which is circumferentially fitted about the rectangular waveguide and insulated therefrom for reflecting back a short circuit at the rear surface of the array of phase shifting elements. These collars provide an improved ground plane between the rear radiating apertures of the phase shifting elements.

With respect to'the plurality of nonreciprocal quarter I waveplates, a pair of these-plates each of which comprises four permanent magnets are placed about the ends of the ferrite rod, and a third plate which comprises a cylindrical quartz rod of larger cross section than the ferrite rod is coupled via a dielectric section to the front end of the ferrite rod. The polarization sensitive RF load is provided by means of a lossy vane positioned at the junction of the ferrite rod and the rectangular waveguide. The reciprocal and nonreciprocal components cooperate to yield a reciprocal phase shifting network which, when excited with a linear polar ized input wave at the back end, will radiate one sense of circular polarization into space at the frontend. The

same sense circularly polarized return wave enters the phase shifting element at its front end-and emerges linearly polarized at the rear radiating aperture. Returning radiation circularly polarized in th'e'oppositesense enters the phase shifting element and is absorbed in the lossy vane. i

A horn is provided for illuminating the back ends 0 the phase shifting elements with radiant energy for transmission therefrom. Each of the phase shifting elements is individually controllable to provide a phase shift to radiation transmitted via one phase shifting element relative to another phase shifting element so that the array functions as a lens for steering and focussing a beam of radiation or, concentric rings of these phase shifting elements may be given specific values of phase shift to provide a microwave lens or spatial filter. Means are also disclosed for utilizing the array of phase shifting elements as a lens in an airport surveillance system.

BRIEF DESCRIPTION OF THE DRAWINGS The aforementioned features and otheradvantages" of the invention are explained in the following description taken in connection with the accompanying drawings wherein:

FIG. I is a plan view partially cut away of a phase with aircraft landing on and alighting from airport runways;

FIG. 5 is a diagrammatic view of one column of phase shifters of the array of FIG. 4;

FIG. 6 is an end view of one of the phase shifters in FIG. 5; and

FIG. 7 is a sectional view of a phase shifter taken along the line 7-7 of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the FIGS. 1, 2 and 3 there are seen a plan view partially cut away, an elevation view sectioned along a longitudinal axis, and an isometric view partially cut away, of a phase shifting element which, in accordance with the invention, comprises a phase shifting section 22, a vane 24, a rear radiator or matching section 26, reciprocal quarter wave plate 28, two nonreciprocal quarter wave plates 30A and 308,

an impedance matching transformer 32 for matching the reciprocal quarter wave plate 28 to the nonreciprocal quarter wave plate 30A and a transformer or radiator 33 which matches the reciprocal quarter wave plate 28 to the variable impedance of free space. This free space impedance varies in the situation where a plurality of phase shifting elements 20 are mounted in an array, such as that of FIG. 4, and the array is scanned.

The phase shifting section 22 comprises a ferrite rod 34 of square cross section and having a square loop magnetic hysteresis characteristic. The rod 34 is overlaid with a thin metallic skin, gold having been used in the preferred embodiment, to provide a structure having the form of waveguide 36. The termini of the rod 34 are portions of the quarter wave plates 30A-B. Four keeper bars 40 having a high magnetic permeability and low reluctance are positioned along the waveguide 36 with one keeper bar 40 on each side of the waveguide 36. The magnetic flux within each keeper bar 40 passes through the ferrite rod 34 thus completing the magnetic circuit. An inner and outer winding 42 and 44 are placed within the space between the keeper bars 40 and the waveguide 36, each of the windings 42 and 44 being coaxial to the waveguide 36. These windings'are utilized to set the magnetic state of the ferrite rod 34, and these magnetic states are retained even after the electrical currents in these windings 42 and 44 are terminated due tothe square loop hysteresis characteristic of the composite magnetic circuit. In this way the magnetic flux which circulates through the keeper bars 40 and the ferrite rod 34 is retained at.a specific value even after the currents in the windings 42 and 44 are terminated, thereby providing a latching feature to the phase shifting section 22.

The phase shifting section 22 operates on the principle of the circularly polarized or Faraday rotator which has been described in an article appearing in the Group on Microwave Theory and Techniques of the Institute of Electrical and Electronic Engineers entitled Circularly Polarized Phase Shifter for Use in Phased Array Antennas by M. C. Mohr and S. R. Monaghan in December 1966. Briefly, the circularly polarized radiation of one sense traveling along the waveguide 36 experiences a phase shift related to the strength of the magnetic field in the ferrite rod 34 while a circularly polarized wave of the opposite sense experiences a different phase shift; thus, this is a nonreciprocal phase shifter. Means for energizing the inner and outer windings 42 and 44 are disclosed in a copending patent application for Phased Array Antenna", Ser. No. 186,128, by V. L. Heeren, J. Howell and C. D. Reis. Briefly, computer generated signals are applied to one of the windings 42 and 44 for driving the keeper bars 40 to an extreme state of the hysteresis characteristic, and then the other winding of the two windings 42 and 44 is energized by a voltage pulse of preset duration to provide a specific voltage time integral for driving the material of the keeper bars 40 to a specific state of magnetization corresponding to a desired phase shift which is to be imparted to radiation propagating through the waveguide 36. At the termination of this voltage pulse, no current is flowing in either of the two windings 42 and 44 and the phase shifting element 22 has now been latched to a specific phase shift.

Each of the quarter wave plates 30A and 308 comprise a set of four permanent magnets positioned around the waveguide 36 with the north pole of one ad- 20 jacent the north pole of a neighboring magnet. Thus, as

seen by the arrows in FIG. 3, flux is provided which circulates in opposite senses through the ferrite rod 34. As a result, orthogonal components of a transverse electric field experience different directions of the impressed magnetic flux and, accordingly, receive different phase shifts to provide the conversion between linear and circular polarization.

The quarter wave plates 30A and 30B convert linear polarization to circular polarization and circular polarization back to linear polarization. Thus, a linearly polarized wave having an electric field in the direction indicated by the arrow 46, propagating in the forward direction through the quarter wave plate 308 is converted to a circularly polarized wave. This circularly polarized wave then propagates through the ferrite rod 34 and enters the quarter wave plate 30A whereupon it is reconverted to a linearly polarized wave. The linearly polarized wave then travels through the transformer 32 to the quarter wave plate 28 which reconverts it to a circularly polarized wave. Uponbeing reflected back from a single bounce" reflecting surface such as a raindrop, the circularly polarized return wave enters the quarter wave plate 28, is converted to a linearly polarized wave, is reconverted to a circularly polarized wave by the quarter wave plate 30A, undergoes a phase shift in the ferrite rod 34, is then converted to a linearly polarized wave having'a direction perpendicular to the arrow 46 and is, accordingly, absorbed in the vane 24. If the circularly polarized wave propagating outwardly from the beam steering element 20 were to reflect off a double bounce" object such as an aircraft, which provides both senses of circular polarization, then polarization, opposite to that provided by the raindrop, upon passing through the three quarterwaveplates 28 and 30A-B, would be polarized in the direction of the arrow 46 and would, accordingly, pass by the vane 24 without being absorbed.

The matching section 26 comprises a rectangular waveguide 48 having a broad wall 50 and a narrow wall 52. Two rods 54,'each composed of preferably a crosslinked polystyrene having a dielectric constant of 2.54 and having a substantially square cross section, are placed within the rectangular waveguide 48 along side each of the narrow walls 52. A metallic tuning post 56 is placed on the broad wall 50, between the two rods 54, to aid in matching the impedance of the waveguide 48 to radiation incident upon its rear aperture 58. A ceramic phase trimmer 59 is placed on the opposite one of the broad walls 50 to provide a phase trimming of the phase shifting element 20. Phase trimming is required to adjust the insertion phase length of all phase shifting elements 20 to approximately the same value when the phase shifting elements 20 are utilized in a lens to be described with reference to FIG. 4. This trimming is required because of random variations in the intrinsic properties of the ferrite rod 34 which cause corresponding insertion phase variations. The ferrite rod 34 is coupled to the waveguide 48 by means of a dielectric slab 60 which has a dielectric constant of preferably 13 and is inserted in the front end of the waveguide 48. The dielectric slab 60 has a tongue 62 which extends towards the center of the waveguide 48 and provides the shape of a step to the dielectric slab 60 to aid in the impedance matching.

The dielectric slab 60 also serves to tune the vane 24 so that reflected energy traveling through the ferrite rod 34 towards the vane 24 and having the electric field polarized, perpendicularly to the arrow 46 is reflected back towards the vane 24. In this connection it is noted that a wave having the electric field in the direction of the arrow 46 propagates in the TE mode and has a waveguide cutoff frequency dependent on the width of the broad wall 50. On the other hand, the cross polarized reflected wave is of the TE. mode and its cutoff frequency is dependent on the width of the narrow wall 52. The frequency of the radiant energy is such that the TE mode propagates while the TE mode is below the cutoff frequency. Due to this cross polarized reflected wave being below the cutoff frequency and further due to the shape of the dielectric slab 60, the aforementioned reflection of the reflected cross polarized wave occurs such that a maximum current is induced at the vane 24 for absorption of the power of radiation reflected from raindrops.

The transformer 32 is a section of a dielectric rod of square cross section and having a dielectric constant of preferably 13. A metallic cylindrical shell 64 provides a waveguide for radiant energy propagating through the transformer 32 and the quarter wave plate 28, and has an inner flange 66 having a central bore of square cross section for mating with the surface of the transformer 32. The forward section of the shell 64 com-- prises a central bore of circular cross section and having a diameter larger than a side wall of the transformer 32. Front portion -70 of the transformer 32 extends into the forward chamber of the shell 66, there being simply an air space 72 between the sides of the front portion 70 and the interior wall of the front chamber of the shell 64. The quarter wave plate 28 is preferably of quartz and is provided with a pair of parallel flat surfaces 76A-B disposed at an angle of approximately 45 degrees with respect to the broad walls 50 of the waveguide 48. There are air spaces 78 between the surfaces 76A-B and the interior wall of the front chamber of the shell 64. The flat surfaces 76A-B provide for the conversion from linear to circular polarizationin the quarter wave plate 28 since a component of the transverse electric field normal to the flat surfaces 76A-B experiences a different amount of dielectric material than does the component of a transverse electric field which is parallel to the flat surfaces 76A-B. Thus, the two perpendicular components of a transverse electric field propagate through the quarter wave plate 28 with different speeds and experience a phase shift relative to driver module 82 comprises means for converting computer type signals received via cable 86 to the appropriate voltage pulses for energizing .the windings 42 and 44. The computer type signals are preferably voltage pulses of preset duration as is required for setting and resetting the state of magnetization of the ferrite rod 34. Such a driver circuit module is described in the aforementioned copending application of V. L. Heeren et al.

Referring now to FIG. 4, there is shown an array 88 of the phase shifting elements 20 with each of the cables 86 of the phase shifting elements 20 being shown connecting with a signal generator 90 which provides the appropriate signals on the cables 86 in response to instructions received on line 92 from a programmer 94 in response to orders provided on line 96 by aconsole 98. Also seen in the figure are a horn 100 for illuminating the rear apertures 58 of the phase shifting elements 20 with radiant energy, a transceiver v102 coupled to the horn 100 for generating signals to be transmitted via the array and for receiving signals incident upon the array 88, and a display 104 for presenting data in signals received by the array 88. The console 98 is seen coupled to the transceiver 102 for communicating data thereto for transmission via the array 88, and it is also seen coupled to the display 104 for selecting the data to be presented.

The signal generator 90 may comprise, by way of example, a plurality of sources of voltage pulses of preset length and switching or multiplexing means for directing specific ones of these pulses to specific ones of the phase shifting elements 20, a specific selection being controlled by the instructions from the programmer 94. Since the phase shifting elements 20 employ the aforementioned latching feature,-the signals on the cables 86 need be applied only when required to reorient or refocus a beam of radiation from the array 88. A suitable form of signal generation apparatus for the signal generator 90 and the programmer 94 is disclosed in the aforementioned copending application of V. L. Heeren et al.

The operation of the array 88 is readily demonstrated in an aircraft traffic control situation as depicted in FIG. 4. Here aircraft 106 are seen landing and taxiing on runways 108. A beam of radiation is directed to suecessive ones of these aircraft for providing information with respect to their locations. The transceiver 102 may comprise a standard form of radar transmitter, duplexer, and receiver which are synchronized to the programmer 94, display 104 and signal generator 90 by means of a timing unit 110. It is also noted that at close ranges of an aircraft 106 to the array 88, a beam 112 of radiation may be focussed as is done with optical lenses by a suitably chosen set of phase shifts for each of the phase shifting elements 20 such that a concave wave front emanates from the array 88 and focusses at the relatively short distance of a nearby aircraft 106 (rather than at infinity) thereby minimizing the chance of reflections from another aircraft 106. Tracking of the aircraft 106 may be done manually by an operator at the console 98, or well-known automatic tracking equipment (not shown) may be utilized in the transceiver 102.

Referring now to FIGS. 5, 6 and 7 there is seen a diagrammatic view in section of a column of the phase shifting elements 20 seen in FIG. 4 with more detailed views of the matching system at the back ends of each of the phase shifting elements 20 being seen in FIGS. 6 and 7. The phase shifting elements 20 are seen positioned such that the narrow walls 52 are disposed in vertical planes while the broad walls 50 are disposed in horizontal planes. The array 88 is seen comprising a front support 114 and a center support 1 which hold the phase shifting elements in their respective positions and a rear support 116, which serves as a ground plane as will be described further. The center support 1 15 also includes electrical sockets 117 for mating with the modules 82 to couple electrical signals thereto from the cables 86 of FIG.. 4.

A collar 118, seen also in FIG. 4, is fitted around the back end of each of the phase shifters and is separated from the outer surface of the waveguide 48 of FIG. 1 by a dielectric inner liner 120 which serves to insulate the collar 118 from the metallic surface of the phase shifting element 20. The collar 1 18 has a depth of onequarter wavelength measured in a direction parallel to the axis of the phase shifting element 20 so that the open circuit presented at the inner edge 122 is reflected back as a short circuit at the outer edge 124. Thus, the rear support 116 which is of an electrically conducting material provides in cooperation with the collars 118 a ground plane from the rear aperture 58 of one phase shifting element 20 to the rear aperture 58 of an adjacent phase shifting element 20. In addition, the collars 1 18 serve as chokes which isolate the cables 86 from picking up RF energy radiated towards the rear support 116 by the horn 100. The collars are held FIG. 7. The pins 126 in cooperation with the short circuit at the ground plane 132 provided by the collars 118 and the tuning posts 56 (seen in FIG. 6) in each of the waveguides 48 provide an improved impedance matching system for coupling radiation between the horn 100 and the array 88. Similar comments apply to an egg crate" or cellular type of impedance matching structure 134 in which metallic walls of each cell separate the radiators 33 (seen in FIG. 3) of adjacent phase shifting elements 20.

It is understood that the above described embodiment of the invention is illustrative only in that the modifications thereof will occur to those skilled in the art. Accordingly, it is desired that this invention is not to be limited to the embodiment disclosed herein but is to be limited only as defined by the appended claims.

What is claimed is:

1. In an array of phase shifting elements, a phase shifting element of said array comprising:

a latching phase shifter;

ement to be positioned adjacent said phase shifting element for receiving said illuminating energy.

2. The phase shifting element according to claim 1 wherein said coupling means is a waveguide, said waveguide being partially filled with a dielectric material, and said waveguide having a tuning post located in an unfilled portion of said waveguide.

3. The phase shifting element according to claim 2 wherein said waveguide of said coupling means has a broad wall and a narrow wall, a portion of said dielectric material being positioned along side one of said narrow walls and a second portion of said dielectric material being positioned along side another narrow wall, and said tuning post being located on one of said broad walls.

4. The phase shifting element according to claim 3 wherein said waveguide and said coupling means have a rear aperture by which radiant energy maybe radiated away from said phase shifting element, said waveguide containing a dielectric slab positioned within a front aperture of said waveguide for coupling radiant energy from said waveguide to said latching phase shifter, said dielectric slab having a tongue-shaped appendage extending from said dielectric slab in a direction towards the center of said waveguide.

5. The phase shifting element according to claim 1 wherein said polarization converting means is a quartz rod enclosed by a metallic waveguide of circular cross section, said quartz rod having a cylindrical form wherein a pair of arcuate surfaces are separated by a pair of planar surfaces, said quartz rod being oriented relative to the polarization of radiant energy propagating from said latching phase shifter to said polarization converting means such that a component of an electric field of said radiant energy is normal to one of said flat surfaces while a second component of said electric field is parallel to one of said flat surfaces.

6. The phase shifting element according to claim 5 further comprising a second and a third polarization converting means, said second and said third polarization converting means each comprising a set of mag nets disposed about an axis of said latching phase shifter and providing magnetic fields directed in planes normal to said axis, the magnets in each of said sets of magnets being oriented to provide magnetic fields directed in opposite directions about said axis.

7. The phase shifting element according to claim 6 wherein said latching phase shifter comprises a ferrite rod enclosed within an overlay of an electrically conducting material, means for establishing a solenoidal flow of electric current around said ferrite rod, and means for conducting a magnetic flux through a circuit from one portion of said ferrite rod via a path external to said solenoidal means to a second portion of said ferrite rod, said magnetic circuit passing through a material having a square loop hysteresis characteristic.

8. The phase shifting element according to claim 1 wherein said latching phase shifter comprises a ferrite rod enclosed within an overlay of an electrically conducting material, means for establishing a solenoidal flow of electric current around said ferrite rod, and means for conducting a magnetic flux in a circuit through said ferrite rod and thence from one portion of said ferrite rod via a path external to said solenoidal means to a second portion of said ferrite rod, said magnetic circuit passing through a material having a square loop hysteresis characteristic.

9. The phase shifting element according to claim 8 wherein said coupling means is a waveguide, said waveguide being partially filled with a dielectric material, and said waveguide having a tuning post located in an unfilled portion of said waveguide.

10. In combination:

a first polarization converting means comprising a circular waveguide, a dielectric rod positioned within said circular waveguide and having a width as measured in one axial plane which is larger than the width as measured in a second axial plane normal thereto for providing differential phase shifts to components of radiation in these two planes;

a rectangular waveguide;

an elongated wave propagating medium consisting of a central portion of ferrite material and two end portions in contact therewith of dielectric material, one of said end portions extending into said circular waveguide to contact said dielectric rod for coupling radiant energy thereto, a second of said end-portions extending into said rectangular waveguide for coupling radiant energy thereto;

means for establishing a solenoidal electric current around said central portion of said wave propagating medium;

means for conducting magnetic flux in a magnetic circuit through said central portion of said wave propagating medium and external to said solenoidal current means, said magnetic circuit passing through material having a square hysteresis loop magnetization characteristic;

a plurality of magnets arranged around said central portion of said wave propagating medium for providing magnetic flux paths in a plane normal to the axis of said elongated wave propagating medium, portions of said flux being oriented in a direction around said propagating medium opposite to the direction of other portions of said flux;

a tuning post positioned along a center line of a wall of said rectangular waveguide; and

a pair of dielectric rods positioned on opposite sides of said tuning post.

11. in combination:

a plurality of phase shifting elements arranged in an array;

a support means for supporting said phase shifting elements in said array, each of said phase shifting elements comprising:

a latching phase shifter;

means connecting with said latching phase shifter for converting circularly polarized radiation to a linearly polarized radiation;

means connected with said latching phase shifter for absorbing radiant energy of one polarization while permitting orthogonally polarized radiant energy to pass through said phase shifting element; and

means for coupling said phase shifting element to a source of illuminating energy, said coupling means being adapted to permit a first one of said phase shifting elements to be positioned adjacent a second of said phase shifting elements for receiving said illuminating energy, Said coupling means comprising a quarter wavelength collar which is insulatedly mounted about an end of said phase shifting element for extending a ground plane of said support means to a radiating aperture of said phase shifting element; and

a plurality of quarter wavelength pins mounted in said support means between adjacent phase shifting elements for affixing said collars to said support means, said quarter wavelength pins extending outwardly from said ground plane towards a source of radiant energy.

12. A phase shifting system comprising:

a plurality of phase shifting elements;

a support means for supporting said phase shifting elements in an array, each of said phase shifting elements comprising a latching phase shifter, means coupled to said latching phase shifter and responsive to radiant energy having a circular polarization of a predetermined sense for absorbing such energy, and waveguide means for coupling said latching phase shifter to a source of illuminating energy;

a plurality of quarter wavelength collars each of which is insulatedly mounted upon respective ones of said waveguide means for providing in cooperation with said support means a ground plane between radiating apertures on said phase shifting elements; and

a plurality of quarter wavelength pins mounted in said support means between adjacent phase shifting elements for affixing said collars to said support means, said quarter wave-length pins extending outwardly from said ground plane towards a source of radiant energy.

13. The phase shifting system according to claim 12 further comprising a signal generator for actuating each of said latching phase shifters to provide a preselected amount of phase shift, said signal generator providing a first signal for resetting said latching phase shifter to a predetermined state and a second signal for setting said latching phase shifter to provide said preselected phase shift.

14. The phase shifting system according to claim 13 further comprising means synchronized to said signal generator for transmitting and receiving radiant energy signals via said array of phase shifting elements. 

1. In an array of phase shifting elements, a phase shifting element of said array comprising: a latching phase shifter; means connecting with said latching phase shifter for converting circularly polarized radiation to a linearly polarized radiation; means connecting with said latching phase shifter for absorbing radiant energy of one polarization while permitting orthogonally polarized radiant energy to pass through said phase shifting element; and means for coupling said phase shifting element to a source of illuminating energy, said coupling means being adapted to permit a second phase shifting element to be positioned adjacent said phase shifting element for receiving said illuminating energy.
 2. The phase shifting element according to claim 1 wherein said coupling means is a waveguide, said waveguide being partially filled with a dielectric material, and said waveguide having a tuning post located in an unfilled portion of said waveguide.
 3. The phase shifting element according to claim 2 wherein said waveguide of said coupling means has a broad wall and a narrow wall, a portion of said dielectric material being positioned along side one of said narrow walls and a second portion of said dielectric material being positioned along side another narrow wall, and said tuning post being located on one of said broad walls.
 4. The phase shifting element according to claim 3 wherein said waveguide and said coupling means have a rear aperture by which radiant energy may be radiated away from said phase shifting element, said waveguide containing a dielectric slab positioned within a front aperture of said waveguide for coupling radiant energy from said waveguide to said latching phase shifter, said dielectric slab having a tongue-shaped appendage extending from said dielectric slab in a direction towards the center of said waveguide.
 5. The phase shifting element according to claim 1 wherein said polarization converting means is a quartz rod enclosed by a metallic waveguide of circular cross section, said quartz rod having a cylindrical form wherein a pair of arcuate surfaces are separated by a pair of planar surfaces, said quartz rod being oriented relative to the polarization of radiant energy propagating from said latching phase shifter to said polarization converting means such that a component of an electric field of said radiant energy is normal to one of said flat surfaces while a second component of said electric field is parallel to one of said flat surfaces.
 6. The phase shifting element according to claim 5 further comprising a second and a third polarization converting means, said second and said third polarization converting means each comprising a set of magnets disposed about an axis of said latching phase shifter and providing magnetic fields directed in planes normal to said axis, the magnets in each of said sets of magnets being oriented to provide magnetic fields directed in opposite directions about said axis.
 7. The phase shifting element according to claim 6 wherein said latching phase shifter comprises a ferrite rod enclosed within an overlay of an electrically conducting material, means for establishing a solenoidal flow of electric current around said ferrite rod, and means for conducting a magnetic flux through a circuit from one portion of said ferrite rod via a path external to said solenoidal means to a second portion of said ferrite rod, said magnetic circuit passing through a material having a square loop hysteresis characteristic.
 8. The phase shifting element according to claim 1 wherein said latching phase shifter comprises a ferrite rod enclosed within an overlay of an electrically conducting material, means for establishing a solenoidal flow of electric current around said ferrite rod, and means for conducting a magnetic flux in a circuit through said ferrite rod and thence from one portion of said ferrite rod via a path external to said solenoidal means to a second portion of said ferrite rod, said magnetic circuit passing through a material having a square loop hysteresis characteristic.
 9. The phase shifting element according to claim 8 wherein said coupling means is a waveguide, said waveguide being partially filled with a dielectric material, and said waveguide having a tuning post located in an unfilled portion of said waveguide.
 10. In combination: a first polarization converting means comprising a circular waveguide, a dielectric rod positioned within said circular waveguide and having a width as measured in one axial plane which is larger than the width as measured in a second axial plane normal thereto for providing differential phase shifts to components of radiation in these two planes; a rectangular waveguide; an elongated wave propagating medium consisting of a central portion of ferrite material and two end portions in contact therewith of dielectric material, one of said end portions extending into said circular waveguide to contact said dielectric rod for coupling radiant energy thereto, a second of said end portions extending into said rectangular waveguide for coupling radiant energy thereto; means for establishing a solenoidal electric current around said central portion of said wave propagating medium; means for conducting magnetic flux in a magnetic circuit through said central portion of said wave propagating medium and external to said solenoidal current means, said magnetic circuit passing through material having a square hysteresis loop magnetization characteristic; a plurality of magnets arranged around said central portion of said wave propagating medium for providing magnetic flux paths in a plane normal to the axis of said elongated wave propagating medium, portions of said flux being oriented in a direction around said propagating medium opposite to the direction of other portions of said flux; a tuning post positioned along a center line of a wall of said rectangular waveguide; and a pair of dielectric rods positioned on opposite sides of said tuning post.
 11. In combination: a plurality of phase shifting elements arranged in an array; a support means for supporting said phase shifting elements in said array, each of said phase shifting elements comprising: a latching phase shifter; means connecting with said latching phase shifter for converting circularly polarized radiation to a linearly polarized radiation; means connected with said latching phase shifter for absorbing radiant energy of one Polarization while permitting orthogonally polarized radiant energy to pass through said phase shifting element; and means for coupling said phase shifting element to a source of illuminating energy, said coupling means being adapted to permit a first one of said phase shifting elements to be positioned adjacent a second of said phase shifting elements for receiving said illuminating energy, said coupling means comprising a quarter wavelength collar which is insulatedly mounted about an end of said phase shifting element for extending a ground plane of said support means to a radiating aperture of said phase shifting element; and a plurality of quarter wavelength pins mounted in said support means between adjacent phase shifting elements for affixing said collars to said support means, said quarter wavelength pins extending outwardly from said ground plane towards a source of radiant energy.
 12. A phase shifting system comprising: a plurality of phase shifting elements; a support means for supporting said phase shifting elements in an array, each of said phase shifting elements comprising a latching phase shifter, means coupled to said latching phase shifter and responsive to radiant energy having a circular polarization of a predetermined sense for absorbing such energy, and waveguide means for coupling said latching phase shifter to a source of illuminating energy; a plurality of quarter wavelength collars each of which is insulatedly mounted upon respective ones of said waveguide means for providing in cooperation with said support means a ground plane between radiating apertures on said phase shifting elements; and a plurality of quarter wavelength pins mounted in said support means between adjacent phase shifting elements for affixing said collars to said support means, said quarter wave-length pins extending outwardly from said ground plane towards a source of radiant energy.
 13. The phase shifting system according to claim 12 further comprising a signal generator for actuating each of said latching phase shifters to provide a preselected amount of phase shift, said signal generator providing a first signal for resetting said latching phase shifter to a predetermined state and a second signal for setting said latching phase shifter to provide said preselected phase shift.
 14. The phase shifting system according to claim 13 further comprising means synchronized to said signal generator for transmitting and receiving radiant energy signals via said array of phase shifting elements. 